Constant velocity ratio universal joint with gothic arch shaped rollers and guide grooves

ABSTRACT

A constant velocity ratio universal joint of the tripod type, comprising an outer joint member (10) with three guide grooves (20), and an inner joint member with arms (13) each carrying a roller (21) which is able to rotate about, move lengthwise of, and tilt relative to the arm, wherein both the external surface (22) of the roller and each side portion of a guide groove (20) engaged thereby is of a gothic arch cross sectional shape to provide for angular contact between roller and guide groove and improve the guidance of the roller so that it remains aligned in the groove for rolling therealong and with the gothic arch section of the roller and/or guide groove side comprising arcuate portions with different centers of curvature, or having part-elliptical or part-involute portions.

BACKGROUND OF THE INVENTION

This invention relates to constant velocity ratio universal joints ofthe tripod type. A joint of the type to which the invention relatescomprises an outer joint member having a rotational axis and three guidegrooves extending parallel to its rotational axis and equallycircumferentially spaced thereabout; an inner joint member disposedinside the outer member, having a rotational axis and three arms equallyspaced about this rotational axis extending radially into the guidegrooves of the outer joint member; each arm carrying a roller having anexternal surface which engages opposed side portions of thecorresponding guide groove so that the roller is constrained to rolltherealong; each roller being able to rotate about, move lengthwise of,and tilt relative to the arm by which it is carried. Such a joint willhereafter be referred to as a tripod joint of the kind specified.

In a tripod joint of the kind specified, the constraint of each rollerto rolling movement along its respective guide groove in the outer jointmember, without tilting relative thereto, means that the joint has areduced frictional resistance to plunge (i.e. relative axial movementbetween the outer and inner joint members) and rotation when the jointis articulated. When the joint rotates in the articulated condition,each roller tilts relative to the arm by which it is carried rather thanrelative to the groove in which it is engaged. It will be appreciatedthat if the roller tilted relative to the groove, it would not be ableto roll along the groove but would have to slide therealong in thetilted condition, which obviously would produce a greater frictionalresistance to such movement.

There have been various proposals for arrangements by which each rolleris carried by its respective arm so as to be able to undergo thenecessary rotational, sliding and tilting movement relative thereto. Forexample, in U.S. Pat. No. 4,379,706 there is disclosed a tripod joint ofthe kind specified wherein each arm has an outer cylindrical surface andeach roller has an inner cylindrical surface, between these two surfacesthere being disposed inner and outer guide rings which haveinterengaging part-spherical surfaces. A needle roller bearing isdisposed between the outer surface of the outer guide ring and theinternal cylindrical surface of the roller. In this arrangement, theroller is able to tilt relative to the arm by virtue of theinterengaging part-spherical surfaces of the inner and outer guiderings. The inner guide ring is able to slide lengthways on the arm. Theroller is able to rotate about the arm by virtue of the needle rollerbearing between the outside of the outer guide ring and the innercylindrical surface of the roller.

A further example of a tripod joint of the kind specified is disclosedin JP-UM Laid Open No. 63-57822. In this joint, each arm of the innerjoint member has a cylindrical surface and each roller comprises innerand outer roller elements with inter-engaging part-spherical surfaces. Aneedle roller bearing assembly is disposed between the internal surfaceof the inner roller element and the cylindrical surface of the arm. Theouter roller element is able to tilt relative to the arm by virtue ofthe interengaging part-spherical surfaces of the inner and outer rollerelements, while both the inner and outer roller elements together areable to rotate about the arm and slide lengthways of the arm, suchrotational and sliding movement together taking place at the needleroller bearing between the internal surface of the inner roller elementand the outer cylindrical surface of the arm.

In JP-UM 63-57822, the outer peripheral surface of the outer rollerelement is toroidal, i.e. it is a surface of rotation, about the axis ofthe roller, of an arc which, in a section through the roller elementviewed lengthwise of the guide groove in the outer joint member, has aradius of curvature smaller than the outer diameter of the outer rollerelement. Each side portion of the guide groove, where it is engaged bythe outer roller element is of "gothic arch" section, comprising twoarcuate portions with different centres of curvature so that the outerperipheral surface of the outer roller element contacts the groove sideportion at two points (although it will be appreciated that when underload the roller/groove engagement is through small elliptical areas ofcontact rather than at true points). This condition, referred to asangular contact, provides for a reduction of friction between the outerroller element and groove when rolling therealong, and also such aconfiguration resists tilting of the outer roller element within thegroove.

In practice the effectiveness of the angular contact between roller andgroove in preventing the roller from tilting is subject to toleranceswhich inevitably are present when these components are mass produced. Ifthe roller element fitted in the groove with no backlash (clearance)whatsoever, then it would be impossible for the roller element to tiltwithin the groove. If, however, as will in practice be the case, theroller element is not a perfect fit in the groove and there is someclearance or backlash therebetween, the roller element will be able totilt within the groove to a small extent. This is particularly a problemwhen the joint is transmitting little or no torque, when the rollerelement is free to tilt until the clearance between it and the groove istaken up. When the joint is transmitting torque, the fact that theroller element is urged into engagement with a side portion of thegroove has the effect that the roller element is brought into alignmentwith the groove. The geometry of the surfaces of the roller element andgroove side portion, engaging with angular contact, is such that anytendency of the roller element to tilt produces a couple which acts onthe roller element to tend to restore it to its aligned orientation.

Since the smoothness of operation of a joint of the kind specified,however, is dependent on the maintenance of the roller elements in or asclose as possible to the correct alignment in the grooves under allconditions of joint operation, it is recognised that if the control ofthe alignment of the roller elements can be improved then jointperformance can be enhanced. It is, accordingly, the object of thepresent invention to provide a tripod joint of the kind specifiedwherein such improved control of the alignment of the roller elementscan be achieved.

SUMMARY OF THE INVENTION

According to the present invention, we provide a tripod joint of thekind specified wherein both the external surface of each roller and eachguide groove side portion engaged thereby have cross sectional shapesincluding portions which are of gothic arch configuration to provide forangular contact therebetween.

Thus, in a joint according to the invention, angular contact between theroller external surface and each groove side portion is provided, butinstead of the cross-section of the roller surface being arcuate itcomprises portions which independently have angular contact with thegroove side portions.

The advantage of this is that better control of roller/groove alignmentcan be maintained. With such a mode of engagement between the roller andguide groove side portion, any tendency of the roller to tilt results inthe establishment of a restoring couple which is greater than therestoring couple established in the case of a roller otherwisedimensionally comparable and arranged for angular contact at the samepressure angle, but with a groove-engaging external surface which insection is a single arc. This will be described in greater detailhereafter with reference to the accompanying drawings.

The gothic arch cross-sectional shape of the external surface of eachroller may comprise portions which are arcuate with different centres ofcurvature. Similarly the gothic arch cross-sectional shape of each guidegroove side portion may comprise arcuate portions with different centresof curvature. The gothic arch shape of the roller external surface maybe truncated to give an increased clearance between roller and guidegroove at the apices of their gothic arch shapes.

Other gothic arch cross-sectional shapes of the engaging surfaces ofeach roller and guide groove can be utilised, as alternatives to thegothic arch shape comprising arcuate portions. In particular, thesurfaces of each roller and/or groove side portion may comprise portionsof part-elliptical or part-involute cross-sectional shape.

When the outer member of a joint of the kind specified is beingmanufactured, which will be done by a forming or extrusion processrather than by machining in view of the difficulty of machining therequired shape of the guide groove side portions, some distortion of thejoint outer member inevitably results from such manufacture andsubsequent heat treatment thereof. Manufacturing tolerances of the outerjoint member and the rollers have to be selected to take account of suchdistortion. However, such distortion usually takes place in a way whichcan be predicted and which leads to a relatively predictable lack ofsymmetry of the guide groove side portions. In a joint according to theinvention, the fact that the external roller surface is not a single arcin cross-section but is a gothic arch shape including, for example,arcuate parts with different centres, gives the possibility for thecross-sectional shape of the roller external surface itself to be madeasymmetrical to match the asymmetric distorted shape of the guide grooveside portions.

Preferably the joint is one wherein each roller is carried on its arm byan inner roller element having a substantially part-spherical externalsurface, engaging a complementary substantially part-spherical internalsurface in the interior of the roller, the inner roller element furthercomprising a cylindrical internal surface whereby it is able to rotateabout and move lengthwise of the arm on which it is carried, preferablywith the interposition of a needle roller bearing assembly.

In a joint according to the invention, the nature of the engagementbetween rollers and their guide groove side portions is of improvedeffectiveness, when the joint is transmitting torque, to resist anytendency of the rollers to tilt within the grooves. However, as abovereferred to, production tolerances necessarily mean that there will besome clearance between each roller and its guide groove in the directiondiametrically of the roller, so that when the joint is not transmittingtorque the roller will tend to move away from the guide groove sideportion it was previously engaging. The roller will then be able to tiltto some extent before the clearances are taken up and it can tilt nofurther. Therefore, in certain circumstances, it may be desirable toprovide further means for preventing the rollers from tilting more thanby a minimal amount. Several examples of such means are described indetail hereafter.

If such additional means is not provided, the rollers are able to tiltwithin the guide grooves to the extent permitted by the clearancestherein. Such tilting of the rollers can give a joint according to theinvention the ability to articulate to an increased angle, provided thatsuch articulation is not a condition which is present for a significantlength of time. In a motor vehicle, maximum joint articulation is causedby maximum jounce and/or rebound of the vehicle suspension, and when thevehicle is in use these are conditions which are never more thantransient. Therefore, it is acceptable if maximum joint articulationrequires the joint rollers to tilt slightly in their grooves.

In joints of the kind specified, maximum articulation angle is usuallylimited by metal to metal contact of the rollers with the inner jointmember. The ability of the rollers to tilt slightly in their groovesgives a joint articulation capability slightly greater than would belimited by such contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawings, of which:

FIG. 1 is a partly sectioned elevation of a joint according to theinvention, in the articulated condition;

FIG. 2 is a partly sectioned end view of part of the joint of FIG. 1,shown in the non-articulated condition;

FIG. 3 is an enlargement of part of FIG. 2.

FIGS. 4A and 4B show diagrammatically further possible roller and guidegroove configurations in a joint according to the invention;

FIG. 5 is a perspective view showing parts of the joint in a conditionprior to assembly;

FIGS. 6 and 7 are views as FIG. 2 showing further embodiments of jointaccording to the invention;

FIG. 8 is an enlarged view of part of FIG. 7, showing the roller in aslightly tilted condition; and FIG. 8A is a further partial enlargementof FIG. 8;

FIG. 9 is a view as FIG. 2 of yet a further embodiment of jointaccording to the invention;

FIG. 10 is a view as FIG. 2 of another embodiment of joint according tothe invention;

FIG. 11 is a longitudinal section of the joint shown partly intransverse section in FIG. 10;

FIG. 12 is yet a further view as FIG. 2 showing a final embodiment ofjoint according to the invention;

FIGS. 13A and 13B show how increased joint articulation is obtainable ifthe rollers are allowed to tilt slightly in their guide grooves; and

FIG. 14 is similar to FIG. 2 but with various details eliminated so asto show more clearly that no needle bearings are present.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to FIG. 1 of the drawings, there is shown a universaljoint of the tripod type, comprising an outer joint member 10 in theform of an elongate cup-shaped component, from whose closed end a stubshaft 11 extends. Disposed within the outer joint member is an innerjoint member 12, of annular form having three circumferentially equallyspaced arms 13 extending radially outwardly therefrom. The interior ofthe inner joint member 12 is splined to have torque transmittingengagement with a splined end portion 14 of a shaft 15, being retainedthereon by a circlip 16. In FIG. 1, the rotational axis of the outerjoint member is indicated at 17, and that of the inner joint member at18, the joint being depicted in the articulated condition wherein theaxes 17, 18 are inclined to one another. Also shown in FIG. 1 is theaxis 19 of one of the arms 13 which is visible in the section shown, theaxis 19 being perpendicular to the axis 18.

The interior of the outer joint member is formed with three equallycircumferentially spaced guide grooves 20, extending parallel to theaxis 17 of the joint member. The guide grooves 20 are engaged byrespective rollers 21 carried by the arms 13 of the inner joint member,the arrangement of guide groove, roller and associated parts being seenmore clearly in FIG. 2.

Referring now to FIG. 2, there is shown one of the guide grooves 20 inthe outer joint member 10. The groove 20 has two opposed side portionswhich are mirror images of one another, to be engaged by diametricallyopposed parts of the roller 21. The roller 21 is of annular form, havingan external surface 22 and an internal surface 23. The external surface22 of the roller is a surface of revolution described by rotating, abouta central axis 24 of the roller, a line in the shape of a truncatedgothic arch as shown in greater detail in FIG. 3. FIG. 2 shows the jointin the aligned condition, wherein the axis 24 of the roller 21 iscoincident with the axis 19 of the arm 13. The internal surface 23 ofthe roller is substantially part-spherical. The roller further comprisesend faces 26, 27 which are planar and perpendicular to the axis 24, theedges of the roller being radiused where the end faces thereof meet theexternal surface 22 of the roller.

The roller is carried on the arm 13 by an inner roller element 28. Thishas a substantially part-spherical external surface 29 which engages theinternal surface 23 of the roller 21, so that the roller is able to tiltrelative to the inner roller element 28. The element 28 furthercomprises an internal surface 30 which is cylindrical, and is supportedon a cylindrical surface 31 of the arm 13 with the intermediary of aneedle roller bearing assembly comprising a plurality of needle rollers32 disposed circumferentially about the arm 13 and extending parallel tothe axis 19 thereof. The needle rollers 32 are retained in positionbetween the arm 13 and the inner roller element 28 by cage rings 33 anda retaining spring ring 34 engaging a groove 35 adjacent the end of arm13.

The roller 21 is thus able to undergo, simultaneously, three differentmovements relative to the arm 13. It is able to rotate about the axis 19of the arm, when the roller 21 together with the inner roller element 28rotate about the axis 19 with minimal frictional resistance as a resultof the presence of the needle rollers 32 interposed between the arm andthe inner roller element. The roller 21 is able to move lengthwise ofthe arm 13, this movement occurring at the interface between theinternal surface 30 of the element 28 and the needle rollers 32. Theroller is able to tilt relative to the arm 13, the tilting movementoccurring at the interengaging substantially part-spherical surfaces 23,29 of the roller and the inner roller element. When the joint isrotating in the articulated condition, all three movements are involved;FIG. 1 shows the joint in such condition wherein the above describedtilting of the roller relative to the inner roller element has occurred,and the inner roller element has moved radially outwardly relative tothe arm 13 and needle rollers 32.

Referring now to FIG. 3 of the drawings, this is a section,perpendicular to the axis of rotation 17 of the outer joint member 10and containing the axis 24 of the roller, which shows in detail theconfiguration of the external surface 22 of the roller and the sideportion it engages of the guide groove 20. The external surface of theroller is a truncated gothic arch shape in this section, comprisingarcuate portions having respective centres of curvature 22A, 22B offsetto opposite sides of the transverse centre plane, indicated at 37C, ofthe roller. The side portion of the guide groove 20 where it is engagedby the roller is a gothic arch shape in section, comprising arcuateportions with respective centres of curvature 37A and 37B also offset onopposite sides of the plane 37C. The radii of curvature of the arcuateparts of the guide groove side portion 37 are slightly greater than theradii of curvature of the arcuate parts of the roller external surface,with the result that contact therebetween is established at two spaced"points" 38, 39 (in practice small elliptical areas when the joint istransmitting torque and deformation occurs as the roller is pressedagainst the groove side portion).

The above described engagement between the roller and guide groove sideportion at two spaced points is the condition generally known as"angular contact". The angles indicated at P between the perpendicularsat the contact points and the roller centre plane 37C are known as thepressure angles. The condition of angular contact between the roller andguide groove has the effect, when torque is being transmitted, that theroller is guided so that it stays in alignment relative to the guidegroove, with its axis 24 perpendicular to the rotational axis of theouter joint member. Any tendency for the roller to tilt in the guidegroove so that its axis inclines to the axis of the outer joint member,in the same sense that axis 19 is inclined to the axis 17 in FIG. 1,results in the establishment of a couple which tends to restore theroller to the correct alignment.

With the illustrated groove and roller configuration, the restoringcouple established if there is any tendency of the roller to tilt isgreater than if the cross-sectional shape of the external surface of theroller were a single arc of a radius chosen to provide angular contactwith the track groove side portion at the same pressure angle. This is aresult of the reduction of the rate at which the surfaces of the rollerand groove side portion diverge from one another with increasingdistance from the contact points therebetween, as they are viewed incross-section.

When the roller attempts to tilt in the track, an increase in pressureangle occurs with a consequent increase in the offset of the contact"points" 38, 39 from the roller central plane 37C. With the gothic archsections of roller and groove, the rate of change of the offset distanceX relative to the rate of change of pressure angle P is greater than canbe achieved with a roller whose external surface is in the section of asingle arc.

In design of a roller and guide groove for angular contact, one wants toachieve a predetermined pressure angle and, in order to providesufficient load carrying capacity, conformity ratio between the localradii of curvature of the guide groove side portions and contactingparts of the roller external surface. Within such constraints, thegothic arch sections of the roller surface and guide groove can providethe improved resistance to tilting of the roller. It can be shown thatwhen the guide groove side portion is of gothic arch cross section andthe external surface of the roller is arcuate in section, it is notpossible to achieve the required conformity of curvature between theroller and groove side portion surfaces to give the necessary loadcarrying capacity, unless the pressure angle is changed adversely.

As shown in FIG. 3, both the external surface of the roller and theshape of the side portion of the guide groove are symmetrical about theplane 37C. The centres of curvature 22A, 22B are equally offset from theplane 37C. However, one problem in the production of the outer jointmembers of tripod joints and the provision of the guide grooves thereinby a forming process is that of distortion, arising from themanufacturing process and from heat treatment. The result of suchdistortion is that the gothic arch cross-sectional shape of the sideportion of the guide groove may be misaligned or non-symmetrical aboutthe plane 37C, so that it is not engaged by the roller with equalpressure angles. This could then lead to scuffing of the roller as itrolls along the guide groove.

If, however, the nature of such distortion can be predicted, it ispossible to make the roller itself asymmetrical so that it engages thegroove side portion correctly. FIGS. 4A and 4B show possible suchdistorted guide groove configurations, and asymmetric rollerconfigurations to engage correctly therewith.

FIG. 4A shows, in a broken line indicated at 137, one possible deviationof the guide groove side portion from the symmetrical configurationthereof indicated at 37. The centre of curvature of the correspondingarcuate part of the gothic arch section of the guide groove side portionis indicated at 137B, offset from the plane 37C by a lesser distancethan the centre of curvature 37A of the undistorted surface part. Tocompensate for such distortion, the centre of curvature 122B of thecorresponding arcuate part of the gothic arch section of the externalsurface of the roller is offset from the plane 37C by a lesser distancethan is the centre of curvature 22A of the other arcuate part of theroller surface.

FIG. 4B shows an alternative condition wherein distortion of the jointouter member has produced a surface 137 whose centre of curvature, at137B, is offset from the plane 37C by a greater distance than is thecentre of curvature 37A of the other part of the gothic arch section ofthe groove side portion. To compensate for this, the centre of curvature122B of the corresponding arcuate part of the gothic arch section of theroller is offset from the plane 37C by a greater distance than is thecentre of curvature 22A of the other arcuate section of the roller'sexternal surface.

Although it is convenient for the gothic arch cross sectional shape ofthe guide groove side portion and of the roller external surface tocomprise respective arcuate portions whose radii and centres ofcurvature can be selected as above described with the possibility ofcompensating for joint outer member distortion, the same benefits interms of improved control of roller alignment can be obtained with othergothic arch surface shapes. In particular, the surfaces of the rollerand/or guide groove side portion where they engage could be ofpart-elliptical or part-involute section. This could lead to a furtherreduction of the rate at which the surfaces of the roller and grooveside portion diverge from one another with increasing distance from thecontact points therebetween, as they are viewed in cross-section.

Referring now to FIG. 5 of this drawings, this shows, in a diagrammaticperspective view, one way in which the roller 21 and the inner rollerelement 28 may be assembled with one another. To enable the internalsubstantially part-spherical surface 23 of the roller to be engaged withthe external substantially part-spherical surface 29 of the inner rollerelement, the roller 21 may have its internal surface relieved in twodiametrically opposed regions 42, 43, extending from one of the endfaces 26 or 27 of the roller halfway to the other end face. The innerroller element 28 is relieved by the provision at each side of twoopposed chamfers, one of which is clearly visible at 44. These enablethe inner roller element 28 to be inserted into the roller 21 in thedirection indicated by arrow 45, when these components are placed in therelative orientation shown with their axes at right angles to oneanother. Thereafter the inner roller element can be moved angularlywithin the roller to the relative orientation which it occupies in theassembled joint, and will remain held thereto under all conditions ofrelative tilting likely to be encountered in use.

An alternative method of assembly is possible if the roller 21 has awall sufficiently thin to enable it, without having to be subjected toexcessive force, to deform elastically to enable it to be "sprung" ontothe inner roller element without requiring the presence of at least oneof the expedients such as the relieved regions 42, 43 and chamfers 44.If a force is applied to the roller in the diametrically opposeddirections indicated by arrows 46, the dimension of the roller in thedirection perpendicuar thereto will be increased slightly, to facilitatethe inner roller elements being inserted therein by application ofsufficient force in the direction of arrow 45. When the substantiallypart-spherical external surface of the inner roller element ispositioned within the internal substantially part-spherical surface ofthe roller, release of the force applied to the roller permits it toresume its circular shape and the inner roller element is then captivetherein.

A further significant aspect of the engagement of the substantiallypart-spherical surfaces of the roller and inner roller element with oneanother is that reduced friction therebetween may be obtainable if theydeviate slightly from truly part-spherical shape. In particular, as thesurfaces are viewed in section as shown in FIG. 1 and FIG. 2 of thedrawings, it is preferable if the external surface 29 of the innerroller element is convexly curved with a radius of curvature slightlyless than the radius of curvature of the concave internal surface 23 ofthe roller. The surfaces then tend to engage over an annular contactarea of width less than the thickness of the roller. This leads toreduced frictional resistance to tilting of the roller relative to theinner roller element as compared with the resistance which would bepresent if the curvatures of the engaging surfaces were different in theopposite sense (i.e. than if the internal surface 23 of the roller had,in the section shown, a radius of curvature slightly less than theradius of curvature of the external surface 29 of the inner rollerelement. In this case, the surfaces would contact over two spacedannular regions). It will be appreciated that to achieve the requiredengagement, one or both of the interengaging surfaces will deviateslightly from being truly part-spherical, being a surface of revolutionof an arc of the appropriate radius about the axis of the roller orinner roller element.

It is possible for one of the engaging part-spherical surface of theroller or inner roller element to be treated with a material having alow coefficient of friction, e.g. a bonded lubricant or a metal orplastics coating. Such surface treatment reduces the resistance to freerotation of the roller resulting from its engagement with the innerroller element. A lower coefficient of friction may exist between theroller and inner roller element than that which exists between theroller and the guide groove which would not be so treated and whichcould have a rougher surface texture.

As above described, the nature of the engagement between the roller andeach guide groove side portion is effective, when the joint istransmitting torque, to resist any tendency of the roller to tilt withinthe guide groove. However, production tolerances necessarily mean thatthere will be some clearance between roller and guide groove in thedirection diametrically of the roller, and when the joint is nottransmitting torque the roller will tend to move away from the guidegroove side portion it was previously engaging. Even with the gothicarch/gothic arch configuration of the surfaces of the roller and guidegroove side portion according to the invention, the roller will then beable to tilt to some extent before clearances are absorbed and nofurther tilting is possible. In a motor vehicle, unless such tilting isprevented, the result may be transmission and generation of noise andvibration under operational conditions involving the transmission of lowor zero torque, and frequent torque reversals. Therefore it may incertain circumstances be desirable to provide the joint with means forpositively preventing the rollers from tilting (although in othercircumstances the improved resistance to roller tilting in a jointaccording to the invention may be adequate without requiring suchadditional provision).

Some embodiments of such additional means for preventing the rollersfrom tilting in the guide grooves in the outer joint member are shown inthe following figures of drawings.

FIG. 6 shows, in a view corresponding to that of FIGS. 2, an outer jointmember 10 whose guide groove is provided, adjacent its side portionsengaged by the external surface of the roller, with guide shoulders 50.The shoulders are engagable with the end face 26 of the roller 21 andwould be arranged such that when the roller is exactly aligned in theguide groove, with its axis perpendicular to the axis of rotation of theouter joint member, there is a very slight clearance between theshoulders and end face of the roller. As soon as the roller begins totilt, it contacts the shoulder and substantial tilting is prevented.Alternatively or in addition, shoulders engagable with the opposite endface of the roller may be provided, as shown in outline at 50A.

FIG. 7 shows an embodiment of joint which is generally the same as thatof FIG. 6, except that the guide shoulders provided by the outer jointmember adjacent the side portions of the guide groove engaged by theexternal surface of the roller have slightly inclined flat or curvedsurfaces 51, engagable with the end face of the roller where the lattermeets the external surface of the roller.

FIG. 8, and its inset FIG. 8A which is a yet further enlargement of thepart A of FIG. 8, show what happens in the embodiment of FIG. 7 when theroller begins to tilt in its guide groove. The shoulder 51 is soconfigured that the roller contacts it over an elongated line ratherthan at a point. This has the effect of spreading the impact forcebetween the roller and shoulder, reducing wear and causing less noise tobe generated.

FIG. 9 shows an embodiment with yet a further means for constraining theroller against tilting relative to the outer joint member. In thisembodiment, the guide groove has no shoulders to constrain the rollerbut the roller has an annular extension part 52 which extends radiallyoutwardly of the joint as a whole, beyond the end of the arm 13. Theguide groove 20 in the outer joint member is provided in its baseportion with a rib 53 extending radially inwardly of the outer jointmember. The rib 53 affords a flat abutment surface 54, facing the end ofarm 13.

The extension 52 of the roller has a planar annular end face 55 which,when the joint is transmitting torque and the angular contact engagementbetween the roller and opposed side portions of the guide groove is suchas to cause the roller axis to remain perpendicular to the rotationalaxis of the outer joint member, is slightly spaced from the surface 54.When the joint is not transmitting torque and the roller is not thusconstrained, the surface 54 can come into contact with one or otherdiametrically opposed part of the end face 55, to prevent the rollerfrom tilting more than by a minimal amount.

FIGS. 10 and 11 of the drawings show an embodiment of joint whereintilting of the roller is prevented by a guide element 70 of sheet metal,e.g. spring steel, which engages the roller and a base portion of theguide groove in the outer joint member. The guide element 70 has a flatbase, which engages the guide groove in the outer joint member, andlimbs 71 extending radially inwardly (of the outer joint member as awhole) therefrom. The base of the guide element is relieved in itscentre at 73, to give clearance for the end of the arm 13 withoutrequiring an increase in the diameter of the outer joint member. Eachlimb 71 extends to meet the outer surface of the roller, and has aninwardly bent tag 72 which engages the radially outermost end face ofthe roller.

As it engages the roller at diametrically opposed parts thereof, and asthe flat base of the guide element is relatively long, the guide element70 can exert a sufficient couple on the roller to prevent the latterfrom tilting in the guide groove without involving large contactpressures where it engages the roller and outer joint member. Thus,although the guide element has to slide axially of the outer jointmember, unacceptable wear does not occur and an undue resistance torolling movement of the roller along the guide groove does not result.

As an alternative to being made of sheet metal, the guide element 70could be moulded of a plastics material.

Referring now to FIG. 12 of the drawings, this shows an embodiment ofjoint according to the invention wherein, instead of the externalsurface of the roller being convex and the side portions of the guidegroove it engages being concave in cross-section, the external surfaceof the roller is concave and the side portions of the guide groove areconvex. The inner joint member, arms thereof, and inner roller elementssupported on the arms by needle roller bearings, are all identical tothe corresponding components of the joints above described and thereforewill not be again described in detail. The illustrated roller, indicatedat 60, has a substantially part-spherical internal surface 61 as abovedescribed, whilst the external surface 62 of the roller is of concavegothic arch section so that the roller as a whole is somewhat of diaboloshape. Opposite side portions of the guide groove are provided withconvex ribs 63 which are of truncated gothic arch shape in theillustrated section, to provide for angular contact in the same mannerabove described with reference to FIG. 3 of the drawings. In thisembodiment, the result once again is that when the joint is transmittingtorque there is a high resistance to tilting misalignment of the rollerin the guide groove, and when torque is not being transmitted the rollercannot tilt to any substantial extent in the groove.

In all the embodiments above described, a needle roller bearing assemblyis interposed between the internal cylindrical surface of each innerroller and the cylindrical surface of the respective arm. It would bewithin the scope of the invention if a plain bearing were provided atthis point, for example in the form of a bearing bush of a suitablematerial such as a plastics or sintered metallic bearing material. Sucha bush may be slidable and rotatable relative to the inner rollerelement, the arm, or both these components. Yet a further possibility isthat the inner roller element 28 itself may be made of such a bearingmaterial so that it engages directly and is able to rotate about andslide lengthwise of the arm 13 with sufficient freedom and without anyinterposed bearing member or assembly (FIG. 4). It may be possible toform an inner roller element of a suitable plastics material by mouldingit directly in situ into the roller, thereby avoiding the necessity forhaving to provide the roller and inner roller element with relievedportions to facilitate assembly thereof (in the manner described withreference to FIG. 5 of the drawings) or for having to spring the rollerand inner roller element together. Such a plastics inner roller elementcould be reinforced by a metal insert.

Although the invention has been described above in relation to a tripodjoint of the kind specified wherein each roller is carried by its armwith the intermediary of an inner roller element, the roller and innerroller element having complementary substantially part-sphericalsurfaces and the inner roller element being able to rotate about andmove lengthwise of the arm, it will be appreciated that the invention inits broadest aspect is also applicable to other types of tripod joint ofthe kind specified. Thus, the advantages of improved control ofalignment of the rollers of the joint in their guide grooves areobtained if the configuration of the engaging parts of roller and guidegroove is applied, for example, to a joint of the kind disclosed in GB 2018 393 referred to hereinbefore. There are other types of tripod jointwherein the rollers are able to rotate about, move lengthwise of, andtilt relative to the arms by which they are carried, and the inventioncan advantageously be applied to such other types of joint.

Referring finally now to FIG. 13 of the drawing, the two parts of thisfigure illustrate how, if there is not provided any means positively forpreventing the rollers of the joint from tilting in the guide grooves,the ability of the rollers to tilt slightly as a result of productionclearances between rollers and grooves can give the joint the ability toarticulate to a slightly greater extent than would normally be the case.

FIGS. 13A and 13B are not sections as FIG. 1 wherein the axes ofrotation of both the inner and outer joint members lie in the plane ofthe drawing. In these figures, the axis of the outer joint member liesin the drawing plane while the axis of the inner joint member isinclined to such plane at the angle which best illustrates the conditionwherein the roller has its minimum clearance from the inner jointmember.

FIG. 13A shows roller 21 in alignment in guide groove 20, when the jointis articulated to its normal maximum angle wherein the roller hascontacted a root portion 13A of arm 13. In FIG. 13B, the roller hastilted to the maximum extent possible in its groove, enabling the jointto articulate by an extra angle equal to the angle by which the rollerhas tilted.

As is referred to above, since in use of a motor vehicle the conditionsrequiring maximum joint articulation are transient, it is notdetrimental if such tilting during maximum articulation produces anincreased resistance to joint rotation and plunge.

What is claimed is:
 1. A constant velocity ratio universal joint of thetripod type comprising an outer joint member (10) having a rotationalaxis (17) and three guide grooves (20) extending parallel to itsrotational axis and equally circumferentially spaced thereabout, eachguide groove having opposed side portions; and inner joint member (12)disposed inside the outer member (10), having a rotational axis (18) andthree arms (13) equally spaced about this rotational axis extendingradially into the guide grooves (20) of the outer joint member; each armcarrying a roller (21) having an external surface (22) which engagessaid opposed side portions of the guide groove (20) into which the armextends so that the roller is constrained to roll therealong; eachroller being able to rotate about, move lengthwise of, and tilt relativeto the arm (13) by which it is carried; wherein the cross-sectionalshape of said external surface of each roller is of a truncated gothicarch shape, and the cross-sectional shape of each guide groove sideportion is of a gothic arch shape different from said truncated gothicarch shape of the roller external surface, said roller external surfaceand each guide groove side portion having angular contact engagementwith one another at two spaced points which lie in said roller externalsurface and guide groove side portion which are parts of said gothicarch shapes.
 2. A joint according to claim 1 further characterised inthat each roller (21) is carried on an arm by an inner roller element(28) said inner roller element having a substantially part-sphericalexternal surface (29) and said roller having a complementarysubstantially part-spherical surface (23) in its interior engaged bysaid internal surface of the inner roller element, the inner rollerelement (28) further comprising a cylindrical internal surface (30)whereby it is able to rotate about and move lengthwise of the arm.
 3. Ajoint according to claim 2 further characterised in that a needle rollerbearing assembly (32, 33) is interposed between the internal cylindricalsurface of each inner roller and a cylindrical surface (31) of each arm.4. A joint according to claim 2 further characterised in that saidroller (21) and inner roller element (28) have relieved portions(42,43,44) enabling the roller and inner roller element to be assembledand their substantially part-spherical surfaces engaged with one anotherwhile they are oriented with their axes at right angles to one another.5. A joint according to claim 2 further characterised in that saidroller (21) and inner roller element (28) are assembled and theirsubstantially part-spherical surfaces engaged with one another byresilient deformation of at least one thereof whilst their axes aredisposed generally perpendicular to one another.
 6. A joint according toclaim 2 further characterised in that said inner roller elementcomprises a bearing material and said internal cylindrical surfacethereof engages directly with a cylindrical surface of the arm.
 7. Ajoint according to claim 2 further characterised in that saidsubstantially part-spherical external surface of the inner rollerelement and said substantially part-spherical interior surface of theroller have a lower coefficient of friction therebetween than thecoefficient of friction between the external surface of the roller andthe guide groove side portions.
 8. A joint according to claim 1 furthercharacterised in that each roller-engaging side portion of each guidegroove comprises at least one shoulder (50,50A, 51) and each roller hasan end face (26) engageable with a respective shoulder to prevent theroller from tilting substantially in the groove when torque is not beingtransmitted.
 9. A joint according to claim 8 further characterised inthat the or each said shoulder (51) is inclined so as to have linecontact with the roller end face when the roller begins to tilt.
 10. Ajoint according to claim 1 further characterised in that each roller hasa part (52) extending radially outwardly of the joint as a whole beyondthe outermost end of the arm by which the roller is carried, and eachguide groove has an abutment surface (54) engageable with an end face(55) of the roller part (52) to constrain the roller from tilting in theguide groove when torque is not being transmitted.
 11. A joint accordingto claim 1 further characterised by a respective guide element (70-73)engaging diametrically opposed parts of each roller and also engaging abase portion of the respective guide groove for sliding movementtherealong, to constrain the roller from tilting in the guide groovewhen torque is not being transmitted.
 12. A joint according to claim 1further characterised in that the external surface (62) of each roller(60) is concave as viewed in section, and the side portions of eachguide groove comprise opposed projecting ribs (63).
 13. A jointaccording to claim 1 further characterised in that the roller externalsurface is asymmetrical about a central plane (37C) of the rollerperpendicular to its axis.